The Effect Of Coagulation On The Pathway Of Coagulation

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Haemostasis occurs in three stages, vascular platelet phase, activation of coagulation cascade producing a clot and initiation of control mechanisms. Coagulation tests are used measure the functions associated with clotting, which involves drawing blood, chelating out the calcium and beginning the clot in a controlled environment, to discover if an individual has a clotting disorder or a factor deficiency. There are many disorders that cause problems with coagulation for example thrombophilia and haemophilia. (Hillyer 2009) http://www.ncbi.nlm.nih.gov/books/NBK265/ The parts in bold are the initiation sites of coagulation. Activated partial thromboplastin time (APTT) measures the intrinsic pathway of coagulation, which is the…show more content…
A link is formed between the intrinsic and extrinsic system due to factor Xa ability to activate factor VII. PT also measures levels of factors I, II, V, VII and X based on how long it takes for the blood to clot, essentially utilised to inspect bleeding difficulties. (Walker 1990) The diagram above shows how the thrombin time (TT) measures time it takes for fibrinogen to convert to fibrin in the presence of thrombin. Abnormalities in TT could be due to lacking fibrinogen, abnormal fibrinogen or an inhibitor to the reaction. Deficiency of fibrinogen commonly due to coagulopathy or liver disease, abnormal fibrinogen can be acquired or inherited, acquired form related to liver disease. TT also used to examine possible bleeding disorders or incorrect blood clot development. (Walker 1990) The clinical significance of APTT, is an effective screening test for those with inherited or acquired deficiencies. Inherited diseases such as haemophilia A and haemophilia B, both have prolonged APTT, due to the absence of intrinsic and common factor pathway. Acquired factor deficiencies are vitamin K deficiency, liver abnormalities and drugs such as warfarin. An elongated APTT not entirely normalized after the addition of normal plasma, but the clotting time is significantly reduced. (Walker 1990) The clinical significance of PT is to measure inherited deficiency diseases for example factor VII deficiency, a bleeding disorder classified by
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